Heat exchanger to facilitate accurate temperature control

ABSTRACT

A heat exchanger has a body with an inside surface and an outside surface forming a hole along a predetermined length of the body, wherein the inside surface is of a predetermined size. Additionally, the heat exchanger has an inlet at one end of the predetermined length and an outlet at another end of the predetermined length. The inlet and outlet disposed on the body facilitate flow of material in and out of the body. In one embodiment, included in the body is a rod, having a number of grooves, being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide a long travel path of the material through the body. The predetermined length is of a length sufficiently long to cause the material to exit with a stable temperature that is insensitive to a small variant of the length.

RELATED APPLICATION

[0001] This patent application claims benefit of priority to provisional patent application No. 60/339,765, titled “AN IMPROVED HEAT EXCHANGER TO FACILITATE ACCURATE TEMPERATURE CONTROL”, filed Nov. 1, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to the field of heat exchangers. More specifically, the invention relates to an improved convective heat exchanger that facilitates precise temperature control.

BACKGROUND OF THE INVENTION

[0003] Recently, inspection methods involving thermal signatures of materials are being utilized, in particular, infrared (IR) detection imaging. A turbine component inspection method utilizing IR imaging involves applying a thermal differential to the component. An example of a turbine component may be a thin or flat object that may be referred to as vanes or blades utilized to cause fluid flow or direct fluid.

[0004] For example, often times, applying a thermal differential involves delivering a thermal stimulus, such as a gas, at a high temperature thermal stimulus to the component, and then, immediately following the high temperature inspection medium, delivering another thermal stimulus, such as the gas, at a cold temperature (i.e., cold, relative to the high temperature thermal stimulus) to the component.

[0005] Often times, in inspecting a turbine component, hot and cold gases are used as thermal stimuli. An example of an IR inspection apparatus may be found in copending U.S. patent application Ser. No. ______, titled “TURBINE COMPONENT INSPECTION SYSTEM”, contemporaneously filed, and having at least partial common inventorship with present application. Furthermore, in order to increase quality of results from such an inspection apparatus, inspection conditions such as, but not limited to, temperature, pressure, humidity, etc. may be required to be identical for various blade types.

[0006] Often times, in order to heat the gas, heat exchangers may be utilized. Heat exchangers are designed to transfer heat between fluids at different temperatures. Examples of common heat exchangers may be a vessel in which hot and cold streams are mixed, two streams at different temperatures separated by a wall or tubes, where conductive heat transfer occurs, and so forth. Furthermore, control of the different temperature streams may increase the cost and difficulty associated with manufacturing these types of heat exchangers.

[0007] Other types of heat exchangers may involve convective heat transfer, where a gas is allowed to flow through an area of high temperatures to heat the gas, such as a common hair dryer. In a common hairdryer, air at ambient temperature is forced through heating elements. As the air flows past the heating elements, the heating elements are hot enough to heat the air to very hot temperatures within a relatively short distance. However, the precise temperature at the outlet of the hairdryer is difficult to predict because typical prior art heat exchangers are designed to maximize the amount of hear transfer, i.e. minimizing the amount of time required to bring a fluid to a desired temperature. Thus, slight variations in length air travels past heating elements and temperature and humidity at an inlet of a heat exchanger having an intrinsic steep gradient of heat exchange, substantially affects the temperature at the outlet.

[0008] Another type of heat exchanger that involves convective heat transfer may be where the gas is allowed to travel through a heated metal pipe. However, here again, for the same reasons discussed earlier, a small variation of the length of the heated metal pipe substantially affects the temperatures of the gas at the outlet of the pipe.

[0009]FIG. 1 illustrates an exemplary graph of convective heat transfer to a gas as it flows through a heated metal pipe, where the metal pipe is heated over its entire length. Shown in FIG. 1 is a graph 100 having heat transfer coefficient as it vertical axis and length down the pipe as it horizontal axis. As illustrated by the graph 100, as gas enters the heated metal pipe at an inlet, a value for local coefficient of heat transfer is infinity at the inlet 101 (i.e., heat transfer is highest at the inlet). In FIG. 1, as the gas continues to flow through the heated metal pipe, the local coefficient of heat transfer diminishes to an asymptotic value (i.e., minimal or no heat transfer is approached) 105. Examples of the principles correlating to the graph of FIG. 1 may be found in Momentum, Heat, and Mass Transfer, by C. O. Bennett and J. E. Myers (3^(rd) ed., 1982).

[0010] Thus, an improved heat exchanger providing a more precise control over the temperature of an exiting fluid, while inexpensive and simple to manufacture, is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like references indicate similar elements and in which:

[0012]FIG. 1 illustrates an exemplary graph of convective heat transfer to a gas as it flows through a heated metal pipe, where the metal pipe is heated over its entire length;

[0013]FIG. 2 illustrates a convective heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention;

[0014]FIG. 3 illustrates a grooved rod to provide a long travel path for a gas within a relatively short linear distance, in accordance with one embodiment of the present invention;

[0015]FIG. 4 illustrates the heat exchanger body with an internal feature to receive a grooved metal rod, in accordance present invention;

[0016]FIG. 5 illustrates an exploded view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention;

[0017]FIG. 6 illustrates a cut-away view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention; and

[0018]FIG. 7 illustrate an alternate embodiment of a heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] In the following description, various aspects of the invention will be described. However, it will be apparent to those skilled in the art that the invention may be practiced with only some or all described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. However, it will also be apparent to one skilled in the art that the invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the invention.

[0020] Various operations will be described as multiple discrete steps in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.

[0021] In various embodiments of the present invention, an improved convective heat exchanger that facilitates precise temperature control is disclosed. This and other advantages will be evident from the disclosure.

[0022] In designing a heat exchanger, if a gas is allowed to flow through a very long heated metal pipe, the temperature of the gas will eventually reach the same temperature of the heated metal pipe. If the temperature of the long metal pipe is precisely known, the temperature is held constant over the entire length of the long metal pipe, and the behavior of the flow (i.e., turbulent, laminar, or transitional), the temperature of the gas at the outlet may also be precisely known. However, the length required to heat a gas convectively might be long enough to make its use difficult, costly, or difficult to manufacture.

[0023] Further, in order to have the gas flow through a very long path (i.e., very long effective length of a metal pipe) while reducing the overall length of the metal pipe, the very long metal pipe may be coiled. A coiled metal pipe provides a long path for the gas flow within a relatively short overall length. But, heating a coiled metal pipe is difficult because all of the surface areas of the coiled metal pipe may dissipate heat into its surroundings, and proper connections between parts may also be difficult to achieve.

[0024]FIG. 2 illustrates a convective heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 2, a convective heat exchanger 200 in the shape of a rectangle, and having, in particular, a predetermined length 201. The heat exchanger 200 has a heat exchanger body 202. The heat exchanger body 202 has an inlet 203 at one end and an outlet 205 at the end opposite of the heat exchanger body 202 and two end caps 207, one at each end of the heat exchanger body 202. The gas to be heated enters through the inlet 203, flows through the entire length of the heat exchanger body 202, and exits through the outlet 205 at a precise temperature.

[0025] Heat may be provided to the heat exchanger 200 by an electric heater (not shown) that is coupled to the heat exchanger body 202. The electric heater heats the heat exchanger body 202 to a predetermined temperature, such as, but not limited to, 400° C. (752° F.). The gas enters the inlet 203 at a temperature below that of the heat exchanger body 202, such as, but not limited to, an ambient temperature of 20° C. (68° F.). The gas flows through the length of the heat exchanger body 202 and exits through the inlet 205 at the same temperature of the heat exchanger 202 i.e., 400° C. (752° F.). The material of the heat exchanger body 202 and the end caps 207 may be any type of thermally highly conductive material, such as, but not limited to, pure copper.

[0026] Utilizing the convective heat transfer principles of gas flowing through a heated tube, the predetermined length 201 of the heat exchanger body 202 may be inadequate to heat the gas to the same temperature of the heat exchanger body 202. However, as will be described in further detail below, the effective length of flow for the gas within the heat exchanger body 202 is made adequate to heat the gas to the same temperature of the heat exchanger 200, in accordance with the present invention.

[0027]FIG. 3 illustrates a grooved rod to provide a long travel or path for a gas within a relatively short linear distance, in accordance with one embodiment of the present invention. Shown in FIG. 3, a metal rod 300 of a predetermined length 305 has grooves 310 machined into its surface. The grooves 310 may be of a threaded type with a flat top, such as, but not limited to, an American Standard Acme threads, and a 10 degrees modified square threads. The size of the grooves 310 may be the size required to allow gas flow. Shown in FIG. 3, grooves 310 are machined to facilitate gas flow; however, it should be appreciated by those skilled in the art that any type of machined groove may be utilized to facilitate the gas flow.

[0028] As will be described in further detail below, the space between the grooves 310 is utilized as a coiled metal pipe, thereby increasing the effective length of flow for the gas. Thus, utilizing the effective length of the path through the grooves 310 and correlating the effective length of the path through the grooves 310 with the principles of convective heating for a gas flowing through a tube determine the predetermined length 305. Furthermore, the predetermined length is then of a length sufficiently long to cause the gas to be exhausted at the outlet 205 at a stable temperature that is insensitive to small variations in effective length of the path through the grooves 310 (in other words, operationally, the temperature is deemed invariant relatively to a small variant length). The predetermined length is based at least upon the thermal properties of various gases as they flow through the heat exchanger 200, such as, but not limited to, the behavior of the gas flowing through the grooves 310 (i.e., turbulent flow, laminar flow, and so forth).

[0029] The material of the metal rod may be any type of thermally highly efficient conductive material that also provides enough mass to reduce the thermal dissipation effects, such as significant temperature drops. An example of the thermally highly conductive material that can efficiently yield the desired mass may be a material, such as, but not limited to, pure copper. Additionally, the metal rod 300 may have a coating of another type of metal to inhibit corrosion from the gas, such as, but not limited to, gold. However, the thickness of the coating is preferably thin enough not to interfere with gas flow, such as, but not limited to, 1000 Angstroms. Furthermore, preferably, the coating is accounted for during design, when practicing the present invention, to ensure that the desired volume of flow is maintained after application of the coating and any subsequent coating (i.e., as the initial coating wears).

[0030]FIG. 4 illustrates the heat exchanger body with an internal feature to receive a grooved metal rod, in accordance with the present invention. Shown in FIG. 4 is the heat exchanger body 202 (shown in FIG. 2) with it end caps 207 and the metal rod 300 removed. As shown in FIG. 4, the heat exchanger body 202 has a hole 405 machined along length of the heat exchanger body 202 to connect the inlet 203 and the outlet 205. The length of the heat exchanger body 202 without the end caps matches the predetermined length 305 of the metal rod 300 (both shown in FIG. 3).

[0031]FIG. 5 illustrates an exploded view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 5, the heat exchanger 200 has the metal rod 300 with the grooves 310 inserted into the hole 405 in the heat exchanger body 202. At each end of the heat exchanger body 200, one of the two caps 207 seals the metal rod 300 inserted into the heat exchanger body 202.

[0032] It should be appreciated by one skilled in the art that the heat exchanger 200 may only have one end cap 207 at one end of the heat exchanger body 202. That is, the hole 405 may not run the entire length of the heat exchanger body 202, but instead, a tapped hole deep enough to accommodate the metal rod 300. Because of the requirement that the gas flow into the heat exchanger 200 at the inlet 203 and exhaust out the outlet 205, the heat exchanger body should be properly sealed to prevent gas leakage.

[0033] Additionally, to ensure proper flow of the gas through the grooves 310 to maximize the effective flow path through the heat exchanger body 202, the diameter of the metal rod 300 and the through hole 405 are closely matched. The extent to which the metal rod 300 and the through hole 405 are matched is that the coefficient of thermal expansion for the metal rod 300 and the heat exchanger body 202 is utilized to insert the metal rod 300 into the heat exchanger body 202. That is, one is heated while the other is cooled before insertion, and allowed to return to ambient temperatures, at which point, a very tight fit will occur. This ensures that the gas will flow through the grooves 310 to reach the outlet 205 and exhaust at the same temperature of the heat exchanger body 200, in accordance with one embodiment of the present invention. Referring briefly back to FIG. 1, the one embodiment of the present invention heats the gas towards the asymptotic value (i.e., minimal or no heat transfer is approached) 105 facilitating heating the gas to highest temperatures, saturation temperatures.

[0034]FIG. 6 illustrates a cut-away view of the heat exchanger that facilitates precise temperature control, in accordance with one embodiment of the present invention. Shown in FIG. 6, the gas at ambient temperature enters the inlet 203, flows through the grooves 310, and exits the heat exchanger 200 at the outlet 205.

[0035] As a result, precise control of temperatures of the gas flowing through a heat exchanger while increasing a

[0036]FIG. 7 illustrates a heat exchanger that facilitates precise temperature control, in accordance with an alternate embodiment of the present invention. Show in FIG. 7 is a portion of a heat exchanger body 710 of a heat exchanger 700, in accordance with this alternate embodiment of the present invention. The portion of the heat exchanger body 710 is shown to detail a heating chamber method. In FIG. 7, the portion heat exchanger body 710 represents one end of the heat exchanger body 202 (shown in FIG. 2), and may represent either end of the heat exchanger body 202.

[0037] Shown in FIG. 7, a number of disks 720 are held together by a center rod 721. The disks 720 are spaced apart at predetermined intervals along the center rod 712. Each of the disks 720 has a notch 725 to facilitate flow of gas between the disks 720. Additionally, the each of the disks 720 is oriented such that the notch 725 of an adjacent disk 720 does not align with the notch 725 of a previous disk 720. The orientation is achieved by rotating each of the disks 720 a predetermined angle about the center rod 730, such as each adjacent disk 720 having the notch 725 oriented such that they are 90 degrees out.

[0038] In FIG. 7, the gas may enter the portion of the heat exchanger body 710 at the inlet 203 and enter a heating chamber 735 (i.e., the space between the disks 720). Because the notches 725 are not aligned, the gas fills the heating chamber 735 before the passing through the notch 725 in the adjacent disk 720. The gas continues to travel down the length of the heat exchanger 700 through the notches, while being heated at each heating chamber 735 (i.e., the space between the disks). Each of the heating chamber helps to heat the gas, and the number of disks 720 is based at least upon a notch size, notch orientation, and temperature for the exhaust gas to achieve at the outlet 205.

[0039] The material of the disks 720 and the center rod 730 are also any type of highly thermally conductive material, such as copper.

[0040] While the present invention has been described with regard to a rectangular heat exchanger, it should be appreciated by those skilled in the art that present invention may be practiced to with different shaped heat exchangers, such as, but not limited to, a heat exchanger in the shape of a cylinder. Additionally, the present invention has been described with gas flowing through the heat exchanger; however, it should be appreciated that the heat exchanger may be modified to accommodate any type of flowing matter, such as, but not limited to, liquids and be within the spirit and scope of the present invention. Different embodiments and adaptations besides those shown and described herein, as well as many variations, modifications and equivalent arrangements will now be apparent or will be reasonably suggested by the foregoing specification and drawings, without departing from the substance or spirit and scope of the invention. While the present invention has been described herein in detail in addition to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full an enabling disclosure of the invention.

[0041] Thus, an improved convective heat exchanger that facilitates precise temperature control has been disclosed 

What is claimed is:
 1. A heat exchanger comprising: a body having an inside surface and an outside surface forming a hole along a predetermined length of the body, wherein the inside surface is of a predetermined size; an inlet at a first end of the predetermined length and an outlet at a second end of the predetermined length, disposed on the body to facilitate flow of material in and out of the body; and a rod, having a plurality of grooves, being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide a long flow path for the material flowing through the body, wherein the predetermined length is of a length sufficiently long to cause the material to consistently exit with a stable temperature that is deemed operatively invariant relative to a small variant of the length.
 2. The heat exchanger of claim 1, wherein the body comprises thermally highly conductive material.
 3. The heat exchanger of claim 2, wherein the body further comprises sufficient mass to reduce thermal dissipation effects, such as significant temperature drops.
 4. The heat exchanger of claim 1, wherein the inside surface and the outside surface forms a cylinder.
 5. The heat exchanger of claim 1, wherein the material is a gas, and the predetermined length is a length calculated based at least upon one or more thermal properties of the gas.
 6. The heat exchanger of claim 5, wherein the one or more thermal properties of the gases comprises a saturation temperature of the gas.
 7. The heat exchanger of claim 1, wherein the plurality of grooves comprises a plurality of threads.
 8. A heat exchanger comprising: a body having an inside surface and an outside surface forming a hole along a predetermined length of the body, wherein the inside surface is of a predetermined size; an inlet at a first end of the predetermined length and an outlet at a second end of the predetermined length, disposed on the body to facilitate flow of material in and out of the body; and a plurality of disks, wherein each disk has a notch, being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide heating chambers for the material flowing through the body, wherein the predetermined length is of a length sufficiently long to cause the material to consistently exit with a stable temperature that is deemed operatively invariant relative to a small variant of the length.
 9. The heat exchanger of claim 8, wherein the plurality of disks with the slots are arranged in such a manner as to facilitate flow of the material between the plurality of disks through the slots.
 10. The heat exchanger of claim 8, wherein the body comprises a thermally highly conductive material.
 11. The heat exchanger of claim 8, wherein the body further comprises sufficient mass to reduce thermal dissipation effects, such as significant temperature drops.
 12. The heat exchanger of claim 8, wherein the inside surface and the outside surface forms a cylinder.
 13. The heat exchanger of claim 8, wherein the material is a gas, and the predetermined length is a length calculated based at least upon one or more thermal properties of the gas.
 14. The heat exchanger of claim 13, wherein the one or more thermal properties of t he gases comprises a saturation temperature of the gas.
 15. A heat exchanger for facilitating precise control of temperature of material flowing through the heat exchanger, comprising: a body having an inside surface and an outside surface forming a hole along a predetermined length of the body, wherein the inside surface is of a predetermined size; an inlet at a first end of the predetermined length and an outlet at a second end of the predetermined length, disposed on the body to facilitate flow of material in and out of the body; means for increasing a length of travel for the material through the body; and means for transferring heat to the material, flowing in and out of the body, to heat the material to a predetermined temperature at the outlet of the body.
 16. The heat exchanger of claim 15, wherein the means for increasing the length of travel comprises means for facilitating flow of the material through a plurality of grooves, being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide a long travel path of the material through the body.
 17. The heat exchanger of claim 15, wherein the means for increasing the length of travel comprises means for facilitating flow of the material between a plurality of disks, each being substantially similar in size to the inside surface, inserted into the hole along the predetermined length to provide heating chambers for the material flowing through the body. 